The Food and Drug Administration says the world's best-selling cancer drug is ineffective against treating breast cancer, dealing a major blow as its manufacturer attempts to keep the drug on store shelves.

"There seems to be this perception that there are all these kinder, gentler treatments for metastatic breast cancer, but I'm not aware of those treatments, said Dr. Kimberly Blackwell of the Duke Cancer Institute.

Avastin is still approved for treating colon, lung, kidney and brain cancer, which the FDA is not challenging.